1. Field of the Invention
This invention relates to methods for detecting at least one gaseous medium in the presence of at least one other gaseous medium, and to gas sensors suitable for use in such methods.
2. Discussion of the Prior Art
It is well known that the electrical conductivities of metal oxide semiconducting materials are sensitive to the presence of various gases or vapors and can be used in sensors to detect their presence. See for example the documents GB-A-2 149 120; GB-A-2 149 121; GB-A-2 149 122; GB-A-2 149 123; GB-A-2 166 244 and GB-A-2 218 523, and papers "The Tin Oxide Gas Sensor and its applications", J. Watson, Sensors and Actuators 54(1984) 29-42; "The Detection and Measurement of CO using ZnO Single Crystals", B. Bott et al., Sensors and Actuators 5(1984) 65-73; "The Role of Catalysis in Solid State Gas Sensors", S. J. Gentry et al, Sensors and Actuators 10(1986) 141-163; "Selectivity in Actuators 12(1987) 425-440; and "Electrical Conduction in Solid State Gas Sensors", J. W. Gardner, Sensors and Actuators 18(1989) 373-387.
All such gas sensors rely on the gaseous medium under observation impinging on a surface of a body of the semiconducting metal oxide material and then undergoing some reaction with it which affects the conductance of the semiconducting metal oxide material, which is detected by means of at least one pair of electrodes which are formed upon the body of semiconducting metal oxide material. Hence their performance can be affected by the presence of substances, gaseous or otherwise (other than the materials to be detected), that affect the surface chemistry of the body of semiconducting metal oxide material. It is important to be able to detect when such spurious effects are occurring.